By Shruti Radhakrishnan/Shubhashree Desikan
The notion of Time travel has always fired up our imagination. There is something about being able to navigate and interact with events — before or after they happen. Is it theoretically possible though? What does it even mean?
Who doesn’t dream of time travel at some point or the other. Everyone has regrets in their life that they want to go back and change, or go into the future and change things there too. Ask Ronald Mallett, a famous proponent of the possibility of time travel, who latched on to the obsession of going back in time because he wanted to save his father, whom he lost at age 10, from dying. While the invention of time travel has to be the coolest Fathers' Day gift ever, it's worth pondering if this is at all possible. Mallett, backed by the science of no less than Albert Einstein, thinks so.
And what if it is possible?
Many ideas, in film and fiction, have explored the possibility of time travel and how playing with time can change the way we perceive it.
Here's Sruthi Radhakrishnan and Shubashree Desikan taking a short detour into time travel in popular culture.
How does science look at time travel?
Look at it this way — time travel is happening all the time. When compared to a year before, we have travelled one year in time, haven’t we? The point is whether we can travel time at a faster or slower rate than say one hour per hour, which is our “normal” rate of time travel. Also, we can ask whether we can reverse this and travel backwards.
The mind boggles, because we are so used to the Newtonian way of thinking, where time is an absolute thing, flowing at the same rate everywhere.
We need to look at how science sees time itself. Einstein brought in a whole new way of thinking about time. According to his Special Theory of Relativity, space and time are just two aspects of the same entity — space-time. And the speed of light sets a limit for how fast things can move. As a result of these two factors, time flows at different rates on objects that travel at different speeds. This is most pronounced when they travel at speeds close to that of light. Time flows at a slower rate on a ship — say — which is moving faster than another.
This gives rise to the so-called twin paradox. If one of two twin sisters is taken on a fast ride for twenty years on a spacecraft, while the other is left on earth, and then brought back, due to the fact that time flows slower on the spacecraft, that twin would have aged less than the other one who was left on earth.
Yet, we know they should be equally old. Much effort was spent in trying to resolve this so-called paradox, until experiments and observations showed that time-dilation is a reality and such a twin taken on a space trip would indeed age less than the twin left behind. There is no paradox there, just our perception of time.
Time can flow faster or slower, and all you have to do is to get on to a vehicle that moves faster or slower than earth to travel in time?
Not exactly. The earth is not moving at the speed of light — far, far slower than that. So, you cannot move slower and expect time dilation to happen. If you moved really fast, you would experience time dilation and would remain young while the world has aged, but when you come back to earth, it is not as though you have reached the “future,” it would still be the present for all concerned.
Physicist and popular science writer Michio Kaku describes the Einsteinian view of time as a river, flowing at different speeds at different places.
According to Einstein’s general theory of relativity, very massive or dense objects could warp the very fabric of space-time around them, causing space-time to flow differently around them. Kaku’s analogous “river” of time in such localities could meander or slow down or speed up. These are places where time travel can take place. What if, for instance the river can loop in on itself and come back to where it started. This kind of solution to Einstein’s equations was found by Kurt Godel.
It’s 2016 now. Does physics see time travel as a possibility?
In 1963, Roy Kerr, who has been given the Crafoord Prize this year, postulated a rotating black hole. Called the Kerr black hole, this is not a singular point as we always picturise the black hole, but a ring of very rapidly rotating neutrons. Unlike a smaller, simpler black hole, one can step into this one without being torn into pieces, only you might emerge in another space-time point where there is a white hole, spewing everything that has gone into the black hole. The connection between the two acts as a bridge in time. Since the Godel solution was known, in physics at least there is no taboo on time travel.
Stephen Hawking objected to it saying that we have not, after all, had tourists from the future, and so it is unlikely that such time travel is possible or at least has been cracked. But perhaps there are machines that can only take you forward in time… Now I many physicists see time travel as a possibility. But not now, sometime in the future!
In movies such as Back to the Future or books like H.G. Wells’ The Time Machine, the protagonists just hop into an object that takes them either back or forward in time. How is the idea of a time machine viewed?
Back to the Future is immensely enjoyable, especially because Spielberg is such a good storyteller. Same thing about H.G. Wells. But the thing is, neither work touches upon the paradoxes that may arise or the complexity of the time machine itself. The only point BTTF touches upon is that if you disturb your past you may end up in a totally different world (a parallel universe?) when you arrive at the present (note how Marty’s father is a loser when the story begins, but as a result of Marty’’s intervention in his past, he turns out, when Marty returns, to be a successful author and the bully neighbour is tamed).
To do H.G. Wells justice, it was far before Einstein and his theories that he wrote the book. So, not much scientific thought existed on time dilation and time travel at the time. In fact, there were even earlier stories than The Time Machine about time travel of that kind, but, at the time, it was a dream; now it’s a possibility.
An interesting thing about time travel is the creation of parallel universes. In Stephen Fry’s Making History, two people — a history grad student and a Jewish physics professor from Oxford decide to go back in time and prevent Hitler from ever being born. What then happens ends up as an example of a parallel universe. The student wakes up in Princeton only to find out that the Nazi party has won the war, and because of their actions, all Jews have been exterminated. The idea here of course, is to say that one shouldn’t mess around with time, and this remains a common trope in science-fiction.
The recently released Tamil film 24subverts this trope of creating a parallel universe that is worse than the existing one. But there are inherent issues with this film’s conception of time travel, too. In the film, which actually was a lot of fun, when Manikandan travels back in time, he grows younger and becomes a baby, having traversed 24 years. This cannot be done — for one thing it will mean that the time machine reverses everything that’s happened as you go back in time, which is extremely difficult — like un-eat the burger you just swallowed or make sure your hair is that the exact same length at that point in time.
Also, it puts a limit on going back in time, which depends on the person — 24 years for Manikandan who is twenty-five years old, 50 for his uncle who is fifty and so on. This is so arbitrary and person-dependent that it does not appeal.
In fact, there is a very physical possibility of travelling in time, using a wormhole. As Interstellar explained, these are shortcuts through spacetime, connecting points that could be a billion light-years apart. It is like a tunnel with its ends at two separate spacetime points. If you could figure out how to accelerate one end of the wormhole to the speed of light or close to it, and then brought it back to the original point, time dilation would cause that end to age slowly compared with the other end as observed by an external observer.
However, to a person entering through one end time flows differently compared to the one observing from outside, and he or she would actually observe the same time that the clock showed at the accelerated end at the time of his or her entering the hole. So, to an external observer, the one moving through the wormhole would have travelled back in time.
Which brings us to Interstellar. To quite an extent, they were able to pull off what they did and make it seem accurate since science still doesn’t know if wormhole travel is possible.
While Interstellar’s wormhole may be more similar to the one Carl Sagan posited in Contact, it’s very interesting how they dealt with time as a concept within and outside a wormhole.Interstellar also weaves in the so-called twin paradox that you mentioned, as Matthew McConaughey’s character Joseph Cooper comes back to Earth to find his daughter Murphy was in her deathbed, while he himself is relatively untouched by time.
Interstellar was one of a kind! Everything explained so well and incorporating the latest scientific thought on Time. You know, they even published a paper on how a spinning black hole would appear to someone orbiting it. It was one of those movies where fiction feeds fact.
Earlier, popular culture would take hints from science and build their own fantastical worlds. To an extent, as far as generic books and movies are concerned, this is still the case. But every once in a while, an Interstellar-like work comes around and we see science and popular fiction working in tandem.
While time travel may not be something we could see in our lifetimes, maybe a time will come when we shouldn’t be too surprised to see our future selves meeting us on the streets.